One process commonly used for in-situ recovery of highly viscous “tar-sand” based hydrocarbons (bitumen) is steam assisted gravity drainage (SAGD). SAGD relies on pairs of horizontal wells arranged such that one of the pair of horizontal wells, called the producer, is located below the second of the pair of wells, called the injector. Recovery of bitumen is accomplished by injecting steam into the injector wellbore. The steam then proceeds from the injector wellbore into the hydrocarbon bearing formation where it creates a steam chamber. As steam is continuously injected into the formation, it enters the steam chamber, migrates to the edge of the steam chamber and condenses on the interface between the chamber and bituminous formation. As the steam condenses, it transfers energy to the bitumen, which improves its mobility by heating it up and decreasing its viscosity. The mobile bitumen and condensed water flows down the edges of the steam chamber and into the producer wellbore. The fluid mixture that enters the producer well is then produced to surface.
One strategy used for preferred injection distribution of steam is to use a slotted liner with a low open area. In this strategy, the active mechanism for providing the improved injection fluid distribution is an increased radial flow resistance due to near well bore divergence losses.
Another strategy is to use a technique called “limited entry”. This technique involves injecting steam into a tubing string which is inside the substantially perforated liner of an injection well. The tubing string is equipped with a limited number of distributed perforations. The active mechanism in this strategy is utilization of the choked-flow phenomenon which limits mass-flow velocity through a restriction to sonic velocity.